1. Field of the Invention
This invention relates to a communication apparatus for transmitting information by modulating carrier waves.
2. Description of the Related Art
FIG. 1 shows a configurational diagram of a conventional telephone exchange system. In FIG. 1, there are shown a main unit 201', telephone lines 202a' and 202b', extension telephones 203, 204 and 205, a fascimile device (FAX) 207', a conversation fee administrating unit 209' and an interface 210, such as RS232C, Centronix and the like. In this configuration, conversation fees used by the system are summed up in the main unit 201', and output to the conversation fee administrating unit 209'.
In the above-described conventional example, however, the conversation fee administrating unit 209' is always required and is dedicated apparatus.
Furthermore, in the prior art, when data are transmitted by digital modulation to a facsimile, a printer, a personal computer and the like, a modem including a digital signal processsor (DSP) is needed. The DSP is a circuit for outputting carrier waves subjected to digital modulation in accordance with input digital data, and is a very expensive apparatus.